cannot mkfs.xfs /dev/sda2 on Ubuntu Server 8.10

I have Ubuntu server 8.10 [64-bit] on a RAID 10 Array (amlost) I followed the guide to partioning my HDDs found here and all was well until I tried to follow the guide for Minimal Ubuntu Server Install I get

Code:

mkfs.xfs: cannot open /dev/sda2: Device or resource busy

when I enter

Code:

mkfs.xfs /dev/sda2

I have partitioned [4] 1TB drives just like the guide says using cfdisk: